According to the National Research Council (1),³ model applications are useful tools to:

5.1.1 Assist in problem evaluation,

5.1.2 Design remedial measures,

5.1.3 Conceptualize and study ground-water flow processes,

5.1.4 Provide additional information for decision making, and

5.1.5 Recognize limitations in data and guide collection of new data.

Ground-water models are routinely employed in making environmental resource management decisions. The model supporting these decisions must be scientifically defensible and decision-makers must be informed of the degree of uncertainty in the model predictions. This has prompted some state agencies to develop standards for ground-water modeling (2). This guide provides a consistent framework within which to develop, apply, and document a ground-water flow model.

This guide presents steps ideally followed whenever a ground-water flow model is applied. The ground-water flow model will be based upon a mathematical model that may use numerical, analytical, or any other appropriate technique.

This guide should be used by practicing ground-water modelers and by those wishing to provide consistency in modeling efforts performed under their direction.

Use of this guide to develop and document a ground-water flow model does not guarantee that the model is valid. This guide simply outlines the necessary steps to follow in the modeling process. For example, development of an equivalent porous media model in karst terrain may not be valid if significant ground-water flow takes place in fractures and solution channels. In this case, the modeler could follow all steps in this guide and not end up with a defensible model.

1.1 This guide covers the application and subsequent documentation of a ground-water flow model to a particular site or problem. In this context, "ground-water flow model" refers to the application of a mathematical model to the solution of a site-specific ground-water flow problem.

1.2 This guide illustrates the major steps to take in developing a ground-water flow model that reproduces or simulates an aquifer system that has been studied in the field. This guide does not identify particular computer codes, software, or algorithms used in the modeling investigation.

1.3 This guide is specifically written for saturated, isothermal, ground-water flow models. The concepts are applicable to a wide range of models designed to simulate subsurface processes, such as variably saturated flow, flow in fractured media, density-dependent flow, solute transport, and multiphase transport phenomena; however, the details of these other processes are not described in this guide.

1.4 This guide is not intended to be all inclusive. Each ground-water model is unique and may require additional procedures in its development and application. All such additional analyses should be documented, however, in the model report.

1.5 This guide is one of a series of standards on ground-water model applications. Other standards have been prepared on environmental modeling, such as Practice E 978.

This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to us

1.6 This guide offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of this guide may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project's many unique aspects. The word "Standard" in the title of this document means only that the document has been approved through the ASTM consensus process.